TYPO3 Extension Categories

All TYPO3 extensions are classified into several predefined categories. These categories do not actually differentiate the extensions. They are more like hints for users about extension functionality. Often, it is difficult for the developer to decide which category an extension should belong to. The same extension can provide PHP code that fits into many categories. An extension can contain Frontend (FE) plugins, Backend (BE) modules, static data, and services, all at once. While it is not always the best solution to make such a monster extension, sometimes it is necessary. In this case, the extension author should choose the category that best fits the extension’s purpose. For example, if an extension provides a reservation system for website visitors, it is probably FE related, even if it includes a BE module for viewing registrations. If an extension provides a service to log in users, it is most likely a service extension, even if it logs in FE users. It will be easier to decide where the extension fits after we review all the extension categories in this article.

Choosing a category for an extension is mandatory. While the TYPO3 Extension Manager can still display extensions without a proper category, this may change and such extensions may be removed from TER (TYPO3 Extension Repository) in the future.

The extension category is visible in several places. Firstly, extensions are sorted and grouped by category in the Extension Manager. Secondly, when an extension is clicked in the Extension Manager, its category is displayed in the extension details.

If an extension’s category is changed from one to another, it does not affect extension functionality. The Extension Manager will show the extension in a different category. So, categories are truly just hints for the user. They do not have any significant meaning in TYPO3.

So, why do we care and talk about them? We do so because it is one of those things that make a good extension. If an extension developer starts making a new extension, they should do it properly from the very beginning. And one of the first things to do properly is to decide where an extension belongs.

So, let’s look into the various extension categories in more detail.

Category: Frontend

Extensions that belong to the Frontend category provide functionality related to the FE. It does not mean that they generate website output. Typically, extensions from the FE category extend FE functionality in other ways. For example, they can transform links from standard /index.php?id=12345 to /news/new-typo3-bookis-out.htm. Or, they can filter output and clean it up, compress, add or remove HTML comments, and so on. Often, these extensions use one or more hooks in the FE classes. For example, TSFE has hooks to process submitted data, or to post‑filter content (and many others).

Examples of FE extensions are source_optimization and realurl.

Category: Frontend plugins

Frontend plugins is possibly the most popular extension category. Extensions from this category typically generate content for the website. They provide new content objects, or extend existing types of content objects.

Typical examples of extensions from the Frontend plugins category are tt_news, comments, ratings, etc.

Category: Backend

Extensions from the Backend category provide additional functionality for TYPO3 Backend. Often, they are not seen inside TYPO3 BE, but they still do some work. Examples of such extensions are various debugging extensions (such as rlmp_ filedevlog) and extensions that add or change the pop-up menu in the BE (such as extra_page_cm_options system extension). This category is rarely used because extensions belonging to it are very special.

Category: Backend module

Extensions from this category provide additional modules for TYPO3 BE. Typical examples are system extensions such as beuser (provides Tools | Users module) or tstemplate (provides Web | Template module).

Category: Services

Services extend core TYPO3 functionality. Most known and most popular service extensions are authentication services. TYPO3 Extension Repository contains extensions to authenticate TYPO3 users over phpBB, vBulletine, or LDAP user databases.

Services are somewhat special and will not be covered in this article. Extension developers who are interested in the development of services should consult appropriate documentation on the typo3.org website.

Category: Examples

Extensions from this category provide examples. There are not many, and are typically meant for beginners or for those who want to learn a specific feature of TYPO3, or features that another TYPO3 extension provides.

Category: Templates

Extensions from this category provide templates. Most often, they have preformatted HTML and CSS files in order to use them with the templateautoparser extension or map with TemplaVoila. Sometimes, they also contain TypoScript templates, for example, tmpl_andreas01 and tmpl_andreas09 extensions. Once installed, they provide pre‑mapped TemplaVoila templates for any website, making it easy to have a website up and running within minutes.

Category: Documentation

Documentation extensions provide TYPO3 documentation. Normally, TYPO3 extensions contain documentation within themselves, though sometimes, a document is too big to be shipped with extensions. In such cases, it is stored separately. There is an unofficial convention to start an extension key for such extensions with the doc_ prefix (that is, doc_indexed_search).

Category: Miscellaneous

Everything else that does not fit into any other category goes here; typical examples are skins. But do not put your extension here if you just cannot decide where it fits. In all probability, it should go into one of the other categories, not into Miscellaneous.

Extension Files

TYPO3 extensions consist of several files. Some of these files have predefined names, and serve a predefined purpose. Others provide code or data but also follow certain naming conventions. We will review all the predefined files in this article and see what purpose they serve. We will look into the files according to their logical grouping.

While reading this section, you can take any extension from the typo3conf/ext/ directory at your TYPO3 installation and check the contents of each discussed file. Some files may be missing if the extension does not use them. There is only one file which is mandatory for any TYPO3 extension, ext_emconf.php. We will start examining files starting from this one.

Common Files

All files from this group have predefined names, and TYPO3 expects to find certain information in them. Hacking these files to serve another purpose or to have a different format usually results in incompatibility with other extensions or TYPO3 itself. While it may work in one installation, it may fail in others. So, avoid doing anything non-standard with these files.

ext_emconf.php

This is the only required file for any TYPO3 extension. And this is the only file that should be modified with great care. If it is corrupt, TYPO3 will not load any extension.

This file contains information on the TYPO3 Extension Manager. This information tells the Extension Manager what the extension does, provides, requires, and conflicts with. It also contains a checksum for each file in the extension. This checksum is updated automatically when the extension is sent to TER (TYPO3 Extension Repository). The server administrator can easily check if anyone has hijacked the extension files by looking into the extension details in the Extension Manager. The modified files are shown in red. Here is a tip. If you (as an extension developer) send your own extension directly to the customer (bypassing TER upload), or plan to use it on your own server, always update the ext_emconf.php file using the Backup/Delete function of the Extension Manager. This will ensure that TYPO3 shows up-to-date data in the Extension Manager.

Here is an example of a ext_emconf.php file from the smoothuploader extension:

<?php
#############################################################
# Extension Manager/Repository config file for ext: ↵ # "smoothuploader"
# Auto generated 29-02-2008 12:36
# Manual updates:
# Only the data in the array - anything else is removed by ↵ # next write.
# "version" and "dependencies" must not be touched!
#############################################################
$EM_CONF[$_EXTKEY] = array(
 'title' => 'SmoothGallery Uploader',
 'description' => 'Uploads images to SmoothGallery',
 'category' => 'plugin',
 'author' => 'Dmitry Dulepov [Netcreators]',
 'author_email' => '[email protected]',
 'shy' => '',
 'dependencies' => 'rgsmoothgallery',
 'conflicts' => '',
 'priority' => '',
 'module' => '',
 'state' => 'beta',
 'internal' => '',
 'uploadfolder' => 0,
 'createDirs' => '',
 'modify_tables' => 'tx_rgsmoothgallery_image',
 'clearCacheOnLoad' => 0,
 'lockType' => '',
 'author_company' => 'Netcreators BV',
 'version' => '0.3.0',
 'constraints' => array(
 'depends' => array(
 'rgsmoothgallery' => '1.1.1-',
 ),
 'conflicts' => array(
 ),
 'suggests' => array(
 ),
 ),
 '_md5_values_when_last_written' => 'a:12:{s:9:...;}',
 'suggests' => array(
 ),
);
?>

The variable _md5_values_when_last_written is shortened in the listing above.